FFS (Fringe Field Switching) or ADS (Advanced Dimension Switch) mode liquid crystal display device is becoming a research hotspot in development of the liquid crystal display device for the advantages of high transmissivity, wide viewing angle, wide color gamut and so on.
As shown in FIG. 1, a plurality of pixel units 9 for display (i.e. for outputting light) are arranged on the array substrate of the FFS mode or ADS mode liquid crystal display device, each pixel unit 9 is provided with a plate electrode 2, a slit electrode 1 is provided above the plate electrode 2, and an insulation layer (not shown) is provided between the plate electrode 2 and the slit electrode 1. The regions between the pixel units 9 (i.e., the peripheral region of the pixel units 9) are used for arranging the gate lines 31, data lines 32, thin film transistors 4 and other structures. The regions between the pixel units 9 correspond to the black matrixes on the color filter substrate and are therefore not used for display (i.e. not outputting light).
The “pixel unit” herein refers to a region for display, that is, a region where the light can be transmitted during displaying (light outputting region). The interval regions between the pixel units are used for arrange other structures such as the gate lines, the data lines and thin film transistors; these regions will not output light when displaying as blocked by the black matrixes, and therefore do not belong to the “pixel units”. The “slit electrode” refers to an electrode structure formed by electrode strips and the slits between the electrode strips arranged alternatively. The “plate electrode” refers to a plate electrode structure used for generating a driving electric field with the slit electrodes. Both the “slit electrode” and the “plate electrode” can be obtained by performing photolithography process on a transparent conductive material layer (such as indium tin oxide). During the photolithography process, besides the slit electrodes and the plate electrodes, some conductive material layer may be remained such that electrical connection structures (for example, electrically connecting the electrode strips of the slit electrodes or electrically connecting the electrodes in different pixel units) may be formed. These electrical connection structures are not considered as a part of the slit electrodes and the plate electrodes, although they are formed simultaneously with the slit electrodes or plate electrodes.
The plate electrode 2 may be a pixel electrode and the slit electrode 1 may be a common electrode; or, the plate electrode 2 may be the common electrode and the slit electrode 1 may be the pixel electrode. Whatever the specific type of the electrodes, as shown in FIG. 1, the plate electrode 2 is normally larger than the pixel unit 9 (i.e. the plate electrode 2 extends to the external of the pixel unit 9), while the slit electrode 1 coincides with or is slightly smaller than the pixel unit 9 (i.e., the boundary of the slit electrode 1 corresponds to or is slightly smaller than the boundary of the pixel unit 9).
The inventors found at least the following problems existing in the prior art: in the FFS mode or ADS mode liquid crystal display device, the slit electrode coincides with or is slightly smaller than the pixel unit, thus the electric field distribution at the edges of the slit electrode will be different from that in the center of the slit electrode. The electric field at the edges of the slit electrode is easily disturbed, and has poor driving capability for the liquid crystal molecules, which results in a low efficiency of the liquid crystal at the edge areas of the pixel units (corresponding to the edges of the slit electrodes), and therefore the transmissivity of the entire display device is lowered.